1. Field of the Invention
The present invention relates to a method for forming electrode patterns of a ceramic substrate; and, more particularly, to a method for forming electrode patterns of a ceramic substrate, in which conductive adhesion patterns are formed on an LTCC substrate through a mask, without having to perform an etching process, thereby improving sticking strength of the electrode patterns due to omission of the etching process.
2. Description of the Related Art
There has been increased a demand for a ceramic substrate formed by applying a thin-film electrode pattern instead of an existing electrode print scheme to a surface layer of an integrated multilayer substrate for a probe card which tests a high frequency module of a mobile communication, a microwave connector, a cable assembly, a semiconductor chip, and so on. In case where the thin-film electrode pattern is applied to the surface layer of the ceramic substrate, the ceramic substrate can be implemented to have a fine pattern, compared to the printed electrode pattern. Further, it is possible to increase plating thickness.
As for a ceramic substrate, an HTCC (High Temperature Co-fired Ceramic) substrate or an LTCC (Low Temperature Co-fired Ceramic) substrate is widely used. Herein, the HTCC substrate is heat-treated at a temperature of 1500° C. or higher to thereby form a multilayer substrate. As for material of the HTCC substrate, alumina of 94% or more is used as main material, and a small amount of SiO2 is used as an additive. As for material of an electrode pattern, tungsten W capable of high-temperature firing is mostly used.
Since such an HTCC substrate is superior in terms of mechanical strength and chemical resistance characteristics, the HTCC substrate is provided with the thin-film electrode pattern on the surface thereof, so as to be widely used as an integrated package. However, an electrode pattern made of high-temperature fired tungsten W has electrical conductance lower than that of Ag, or Cu, and thus it has inferior high frequency characteristics and has coefficient of thermal expansion higher than two times that of a silicon semiconductor device, which causes an obstacle to the application field requiring matching of coefficient of thermal expansion.
Contrary to this, an LTCC substrate is heat-treated at a temperature of 900° C. or lower to thereby form a multilayer substrate. In order to use the LTCC substrate at a temperature of 900° C. or lower, a large amount of SiO2 having a low melting point is used, and alumina is relatively less used. As the firing temperature becomes 900° C. or lower, Ag, or Cu may be used as material of an electrode pattern. Resistors, inductors and condensers of being passive components are incorporated into the substrate, so that the substrate can be widely used for miniaturization, convergence, and modularization, and high-frequency of electric components
However, since the LTCC substrate contains a large amount of SiO2, a surface layer of the substrate containing SiO2 is easily etched in an etching process using strong acid chemicals like HF, or strong base chemicals like KOH, which causes degradation in sticking strength of a thin-film electrode pattern formed on the surface layer of an LTCC substrate.
That is, in the prior art, in order to improve adhesion between the LTCC substrate and the electrode pattern, a conductive adhesion layer, for example, Ti layer, is formed on a front surface of the LTCC substrate, and then the Ti layer is etched to be as large as the electrode pattern. However, since an etchant used at the time of etching the Ti layer corresponds to strong acid chemicals like HF, or strong base chemicals like KOH, the surface layer of the LTCC substrate containing a large amount of SiO2 is easily etched by the etchant. In addition, an undercut is produced between the Ti layer and the surface layer of the LTCC substrate, and between the Ti layer and a plating layer formed thereon, which causes difficulty in forming a thin-film electrode pattern. Even if a thin-film electrode pattern is formed, sticking strength is reduced.